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United States Patent |
5,026,800
|
Kimura
,   et al.
|
June 25, 1991
|
Water-absorbent resin and production process
Abstract
Water-absorbent resins having an average particle diameter of 100 to 600
.mu.m and a particle diameter distribution of 0.35 or less are prepared by
polymerizing an aqueous solution of a water-soluble ethylenically
unsaturated monomer, pulverizing and sieving the gel-like polymer so
obtained, and crosslinking the surface of the polymer powder. In an
alternative process, an aqueous solution of the monomer having a viscosity
greater than 15 cps is dispersed in a hydrophobic organic solvent and
polymerized to obtain a polymer powder, and the surface of the polymer
powder is crosslinked.
Inventors:
|
Kimura; Kazumasa (Nara, JP);
Nagasuna; Kinya (Hyogo, JP);
Namba; Takashi (Osaka, JP);
Kadonaga; Kenji (Hyogo, JP);
Miyake; Koji (Osaka, JP);
Shimomura; Tadao (Osaka, JP)
|
Assignee:
|
Nippon Shokubai Kagaku Kogyo Co., Ltd. (Osaka, JP)
|
Appl. No.:
|
371175 |
Filed:
|
June 26, 1989 |
Foreign Application Priority Data
| Jun 28, 1988[JP] | 63-158086 |
| Jul 04, 1988[JP] | 63-164940 |
| Oct 13, 1988[JP] | 63-255866 |
Current U.S. Class: |
526/200; 526/213; 526/317.1; 526/318.1 |
Intern'l Class: |
C08F 002/08; C08F 020/06; C08F 120/06 |
Field of Search: |
526/201,200,213,317.1,318.1
|
References Cited
U.S. Patent Documents
4683274 | Jul., 1987 | Nakamura et al. | 526/216.
|
4732968 | Mar., 1988 | Obayashi et al. | 528/490.
|
4734478 | Mar., 1988 | Tsubakimoto et al. | 527/300.
|
4880888 | Nov., 1989 | Obayashi et al. | 526/209.
|
Foreign Patent Documents |
51-125468 | Nov., 1976 | JP.
| |
52-14689 | Feb., 1977 | JP.
| |
53-15959 | May., 1978 | JP.
| |
55-84304 | Jun., 1980 | JP.
| |
58-180233 | Nov., 1983 | JP.
| |
59-189103 | Nov., 1984 | JP.
| |
60-18690 | May., 1985 | JP.
| |
61-16903 | Jan., 1986 | JP.
| |
61-43606 | Aug., 1987 | JP.
| |
Primary Examiner: Schofer; Joseph L.
Assistant Examiner: Weber; Tom
Attorney, Agent or Firm: Armstrong, Nikaido, Marmelstein, Kubovick & Murray
Claims
We claim:
1. A process for producing a water absorbent resin wherein an aqueous
solution of an acrylic or sulfonyl acid, or their salts, having a
viscosity of 15 to 5,000 cps, determined by a Brookfield rotational
viscometer (25 C, 0.6 rpm), using a sucrose fatty acid ester and/or a
polyglycerol fatty acid ester as dispersing agent, is polymerized to
obtain a gel-like water containing polymer, said gel-like water containing
polymer is dried, the dried polymer is pulverized, and sieved to obtain a
polymer powder having an average particle diameter of 100 to 600 .mu.m and
a particle diameter distribution of 0.35 or less (logarithmic standard
deviation), and the surface of said powder is crosslinked.
2. A process for producing a water absorbent resin wherein an aqueous
solution of an acrylic or sulfonyl acid, or their salts, having a
viscosity of 15 to 5,000 cps, determined by a Brookfield rotational
viscometer (25 C, 0.6 rpm), using sucrose fatty acid ester and/or a
polyglycerol fatty acid ester as dispersing agent, is dispersed and
suspended in a polymerization-inert hydrophobic organic solvent, and
polymerized using an initiator for radical polymerization and the polymer
obtained is dried to a polymer powder having an average particle diameter
of 100 to 600 .mu.m and a particle diameter distribution of 0.35 or less
(logarithmic standard deviation), and wherein the surface of said polymer
powder is crosslinked.
3. A process for producing a water absorbent resin wherein an aqueous
solution of an acrylic or sulfonyl acid, or their salts, having a
viscosity of 5,000 to 1,000,000 cps, determined by a Brookfield rotational
viscometer (25 C, 0.6 rpm), is dispersed and suspended in a
polymerization-inert hydrophobic organic solvent, using only a sucrose
fatty acid ester as a dispersing agent, and polymerized using an initiator
for radical polymerization, and the polymer obtained is dried to a polymer
powder having a ratio of 1.5 to 20 between average particle length and
average particle breadth and having a non-angular, non-spherical shape,
and wherein the surface of said polymer powder is crosslinked.
4. A process for producing a water-absorbent resins as claimed in claim 3,
wherein the length of the particle is in the range of 100 to 10,000 .mu.m,
and the breadth of the particle is in the range of 10 to 2,000 .mu.m.
5. A process for producing water-absorbent resins as claimed in claims 1,
2, 3 or 4 wherein the water content of a polymer powder is less than 10
weight %.
6. A process for producing water-absorbent resins as claimed in claims 1,
2, 3 or 4, wherein, when being treated with crosslinking, an agent having
in the molecule two or more of a group reactive for a functional group of
the polymer powder is used.
7. A process for producing water-absorbent resins as claimed in claim 6,
wherein the crosslinking agent is used in form of a treatment solution
prepared by mixing this agent with water and a hydrophilic organic
solvent.
8. A process for producing water-absorbent resins as claimed in claim 7,
wherein the composition proportions of a crosslinking agent, water, and a
hydrophilic organic solvent are adjusted as, against the polymer powder,
0.005.about.20 weight %, 0.1.about.5 weight %, and 0.01.about.6 weight %,
respectively.
9. A process for producing water-absorbent resins as claimed in claim 7,
wherein a polymer powder is mixed with a treatment solution, then warmed
at 40.degree..about.250.degree. C. and the surface of above-described
polymer powder is treated with crossliking.
Description
BACKGROUND OF THE INVENTION
This invention relates to a water-absorbent resin and a process for
producing this resin. In detail, it relates to a water-absorbent resin
having average particle diameter in a specially defined range, narrow
range of particle distribution, and a surface of uniformly improved
quality and, in particular, being superior in water absorption capacity,
water absorption rate, suction force, and gel strength etc., showing that
water absorption properties are in good balance, showing that an amount of
elution of water-soluble resin (hereinafter referred to as water-soluble
component) is only small, and being very suitable as sanitary materials,
and also, a process for producing the water-absorbent resin. Furthermore,
this invention relates to a water-absorbent resin of a new, novel type
showing angle-lacking, non-sphere, being superior in handling and
treating, and having a surface of uniformly improved quality, and a
process for producing the water-absorbent resin.
Hitherto, an attempt has been carried out to use a water-absorbent resin as
an absorbent sanitary material for absorbing body fluids such as a
sanitary cotton, a disposable diaper, and the like. There have been known,
as water-absorbent resins for this purpose, a hydrolyzed
starch-acrylonitrile graft polymer (Japanese Official Patent Gazette,
shouwa No. 49-43395), a neutralized starch-acrylic acid graft polymer
(Japanese Official Patent Provisional Publication, shouwa No. 51-125468),
a saponified vinyl acetate-acrylic acid ester copolymer (Japanese Official
Patent Provisional Publication, shouwa No. 52-14689), a hydrolyzed
acrylonitrile or acrylamide copolymer (Japanese Official Patent Gazette,
Shouwa No. 53-15959), and crosslinked products of these polymers, a
crosslinked product of a partially neutralized polyacrylic acid (Japanese
Official Patent Provisional Publication, Shouwa No. 55-84304) and others.
Incidentally, as properties to be wanted for water-absorbent resins, are
cited high water absorption capacity, a water absorption rate, and high
gel strength of water-contained swelling gel when the resins are coming in
contact with aqueous liquid, and superior suction force to suck up water
from a basic material containing aqueous liquid. These properties hitherto
have been in a poor balance. That is, these properties are not in directly
proportional relation, in particular, water absorption capacity and water
absorption rate or gel strength and suction force are in reversely
proportional relation, so that there has been found a trend that, as the
water absorption capacity increases, other properties decrease. When some
resins of a high water-absorbent capacity come in contact with aqueous
liquid, aqueous liquid does not spread over the whole part of a
water-absorbent resin and the resins form lumps, that is, what we call
fish-eyes, so that an extreme lowering of a water absorption rate is
observed. Also, in a case of that these water-absorbent resins are used
for an absorption body of sanitary materials, the above-described
water-soluble component being contained in the water-absorbent resins
affects on the absorption capacity of an absorption body, liquid-spreading
in a absorption body, and so on. Especially, as the water-absorption
capacity for a water-absorption resin increases, elution of a
water-soluble component increases in amount, so that there has been found
a problem that the resin can not properly used as sanitary materials.
As methods to improve the above-described properties with maintaining their
good balance, there have been proposed methods to improve such properties
as a water absorption rate etc. by crosslinking the surface of an obtained
water-absorbent resin, without giving damage for water absorption capacity
which the water-absorbent resin itself has. They are a method wherein a
water-absorbent resin being dispersed in a hydrophilic organic solvent or
a hydrophobic organic solvent in presence of water and undergoing to react
in addition of a crosslinking agent (or its aqueous solution) (Japanese
Official Patent Gazette, shouwa Nos. 61-48521 and 60-18690) and a method
wherein a water-absorbent resin powder was mixed with a crosslinking agent
or a liquid composition containing a crosslinking agent to treat with heat
(Japanese Official Patent Provisional Publication, shouwa Nos. 58-180233,
59-189103, and 61-16903) and so on.
In these cases, of importance are uniform dispersion of a crosslinking
agent over the surface of a water-absorbent resin and proper permeation
into a neighborhood of the surface and, in addition, it is liked that the
process is of advantage to industry. However, hitherto known methods have
had problems in these points. That is, in the method wherein a
water-absorbent resin being dispersed in a solvent and undergoing a
crosslinking reaction, a large amount of solvent is required and so, its
recovery process is of disadvantage to industry. Especially, in a case
being carried out in a hydrophobic organic solvent, distribution of a
crosslinking agent on the surface of a water-absorbent resin is apt to
become ununiform, so that the crosslinking of surface becomes ununiform.
In the other hand, the method wherein a water-absorbent resin is mixed
with a liquid component containing a crosslinking agent and treated with
heat, is of great advantage to industry, and however, in a case of that
particle diameter of a water-absorbent resin is small or distribution of
particle diameter is broad, there was found a case that, though being
affected on a treatment solution mixing with the water-absorbent resin
powder, the powder meets together making a large lump (a fish-eye) and so,
it is rather hard to crosslink uniformly the surface. Furthermore, though
by doing these treatments such properties as water absorption rate and
suction force are somewhat improved, but the improvement is still
insufficient and, in particular, elution of a water-soluble component
could not be prevented. Thus, has not yet found a method sufficiently
satisfied in point of that various kinds of properties of a
water-absorbent resin are improved maintaining good balance of properties.
BRIEF SUMMARY OF THE INVENTION
Under these circumstances, the first object of this invention is to provide
a water-absorbent resin, wherein the average particle diameter being in a
specially defined range, the particle diameter distribution being narrow,
the surface being uniformly improved, and in particular, to provide a
water-absorbent resin wherein the water absorption capacity, water
absorption rate, suction force, and gel strength being superior and an
amount of a water-soluble component being small, and a process for
producing this resin.
The second object of this invention is to provide a water-absorbent resin
wherein the shape being angle-lacking, non-sphere, new and novel type, and
the surface being uniformly improved in quality, and a process for
producing this resin.
These objects are attained by crosslinking the surface of a water-absorbent
polymer powder wherein the average particle diameter being in
100.about.600 .mu.m, the particle diameter distribution being 0.35 or less
of a logarithmic standard deviation value, .sigma..sub..zeta., or a
water-absorbent polymer powder wherein a ratio between average length and
average breadth being 1.5.about.20 and showing an angle-lacking,
non-sphere shape.
As methods to obtain a water-absorbent polymer powder having the
above-described average particle diameter and particle diameter
distribution in this invention, although there have been shown, as
examples, a method of an aqueous solution polymerization followed by
pulverization and classification to fit in a range of the above-described
average particle diameter and particle diameter distribution and a method
of reverse-phase suspended polymerization under specified conditions, in
order to obtain in a good yield a water-absorbent polymer powder having
the above-described average particle diameter and particle diameter
distribution and a new, novel shape, the most preferable method is to take
a system where, when a reverse-phase suspention polymerization is carried
out by using a radical polymerization initiator under conditions that a
water-soluble ethylenically unsaturated monomer or its aqueous solution is
suspended and dispersed in a hydrophobic organic solvent, the viscosity of
an aqueous solution of the water-soluble ethylenically unsaturated monomer
determined by a Brookfield rotatory viscosinmeter is adjusted in a value
of 15 cps or more and a sucrose fatty acid ester and/or polyglycerol fatty
acid ester are used as dispersing agent.
In performing the above-described production process, if the viscosity
defined as above is adjusted in a range of 15.about.5,000 cps, is obtained
in good yields a polymer powder having an average diameter of
100.about.600 .mu.m and an index (a logarithmic standard deviation) of
0.35 or less which represents particle diameter distribution.
Furthermore, in performing the above-described production process, if the
viscosity defined as above is adjusted in a range of 5,000.about.1,000,000
cps and, as a dispersing agent, a sucrose fatty acid esters is only used,
is obtained in good yields a polymer powder wherein the ratio between
length and breadth being in a range of 1.5.about.20 and the shape being
non-sphere without angle.
As examples of a water-soluble ethylenically unsaturated monomer
constituting a water-absorbent resin in the present invention, are cited
monomers of anionic character such as acrylic acid, methacrylic acid,
crotonic acid, maleic acid and its anhydride, fumaric acid, itaconic acid,
and 2-(meth)acryloylethanesulfonic acid, and
2-(meth)acryloylpropanesulfonic acid, and
2-(meth)acrylamido-2-methylpropanesulfonic acid, vinylsulfonic acid,
styrenesulfonic acid and the like and their salts; monomers containing
nonionic hydrophilic substituent such as (meth)acrylamide, N-substituted
(meth) acrylamides, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)
acrylate, methoxypolyethylene glycol (meth)acrylate, polyethylene glycol
(meth)acrylate and the like; monomers of cationic character such as
N,N'-dimethylaminoethyl (meth)acrylate, N,N'-diethylaminoethyl
(meth)acrylate, N,N'-diethylaminopropyl (meth)acrylate,
N,N'-dimethylaminopropyl (meth)acrylamide, and the like and their
quaternary salts. These compounds can be used as alone or mixture of two
or more compounds. Preferable are a kind of compound or a mixture of two
or more compounds chosen from the following three groups of compounds:
(meth)acrylic acid, 2-(meth)acryloylethanesulfonic acid,
2-(meth)acrylamido-2-methylpropanesulfonic acid, and their salts; and
N,N'-dimethylaminoethyl (meth)acrylate and their quaternary salts; and
methoxypolyethylene glycol (meth)acrylate and (meth)acrylamide. Although
the monomer concentration in an aqueous monomer solution is generally
variable in a wide range, the preferred range is from 20 weight % up to
saturation.
The water-absorbent polymer powder used for the present invention comprises
a self-crosslinking type prepared in absent of a crosslinking agent and a
type co-polymerized during polymerization with a small amount of
crosslinking agent, which has polymerizable unsaturated groups or reactive
functional groups. As examples of the crosslinking agents are cited
N,N'-methylene-bis(meth)acrylamide, N-methylol(meth)acrylamide, ethylene
glycol (meth)acrylate, polyethylene glycol (meth)acrylate, propylene
glycol (meth)acrylate, polypropylene glycol (meth)acrylate, glycerol
tri(meth)acrylate, glycerol mono(meth)acrylate, polyfunctional metal salts
of (meth) acrylic acid, trimethylolpropane tri(meth)acrylate,
triallylamine, triallyl cyanulate, triallyl isocyanulate, triallyl
phosphate, glycidyl (meth)acrylate. As examples of agents having reactive
functional groups for example, in a case that a monomer has a carboxyl
and/or carboxylate group, polyhydric alcohol derivatives such as ethylene
glycol, diethylene glycol, triethylene glycol, tetraethylene glycol,
polyethylene glycol, glycerol, polyglycerol, propylene glycol,
diethanolamine, triethanolamine, polyoxypropylene,
oxyethylene-oxypropylene block co-polymer, pentaerythritol, and sorbitol;
polyglycidyl derivatives such as ethylene glycol diglycidyl ether,
polyethylene glycol diglycidyl ether, glycerol polyglycidyl ether,
diglycerol polyglycidyl ether, polyglycerol polyglycidyl ether, sorbitol
polyglycidyl ether, pentaerythritol polyglycidyl ether, propylene glycol
diglycidyl ether, and polypropylene glycol diglycidyl ether; aziridine
derivatives and related compounds such as 2,2-bishydroxymethylbutanol-tris
[3-(1-aziridinyl) propionate], 1,6-hexamethylene-diethylene urea, and
diphenylmethane-bis-4,4'-N,N'-diethylene urea; haloepoxyl compounds such
as epichlorohydrin and .alpha.-methylchlorohydrin; polyaldehydes such as
glutar aldehyde and glyoxal; poly amine derivatives such as ethylene
diamine, diethylene triamine, triethylene tetramine, tetraethylene
pentamine, pentaethylene hexamine, and polyethylene hexamine;
polyisocyanates such as 2,4-toluylenediisocyanate and
hexamethylenediisocyanate; polyvalent metal salts such as aluminium
chloride, magnesium chloride, calcium chloride, aluminium sulfate,
magnesium sulfate, and calcium sulfate. Subject to consideration upon
reactivity, these crosslinking agents can be used as a mixture of more
than two, but it is usually preferable to use a crosslinking agent having
polymerizable unsaturated groups. An amount of use of these agents is in
general about 0.001.about.1.0 mol. for a water-soluble ethylenically
unsaturated monomer.
The most preferable way of obtaining the polymer profitable for the present
invention is that the viscosity of an aqueous solution of water-soluble
ethylenically unsaturated monomer is adjusted at a value of 15 cps or more
when determined with a Brookfield rotatory viscometer (25.degree. C., 0.6
rpm) (this sort of viscosity is hereinafter referred to as, simply,
viscosity) and that the reverse-phase suspension polymerization is
performed using a sucrose fatty acid ester and/or a polyglycerol fatty
acid ester as a dispersing agent. If the viscosity being below 15 cps, the
particle obtained is small in average particle diameter and broad in
distribution of particle diameter.
In a method of the present invention wherein a previously-described,
specially defined dispersing agent being used, the viscosity of an aqueous
solution of water-soluble ethylenically unsaturated monomer being adjusted
in a range of 15.about.5,000 cps, a water-absorbent polymer of sphere
shape being suitable for use in the present invention and having an
average particle diameter in a range of 100.about.600 .mu.m depending upon
viscosity and very narrow distribution of particle diameter can be
obtained. Generally under the same condition, the higher the viscosity of
an aqueous solution of a monomer becomes, the larger an average particle
diameter of the resin obtained becomes, and polymer of various average
particle diameters can be obtained with such a simple procedure as an
adjustment of viscosity.
Although a preferable average particle diameter of a water-absorbent resin
obtained is different depending upon a use, for instance, in a case being
used as sanitary materials, the average particle diameter is usually in a
range of 100.about.600 .mu.m, more preferably about 150.about.400 .mu.m.
The particle of this kind is obtainable when the viscosity of an aqueous
solution being adjusted in a range of 15.about.5,000 cps, more preferably
20.about.3,000 cps. In addition, a water-absorbent polymer obtained
according to this method shows very narrow distribution of particle
diameter.
For instance, when particle distribution is plotted in a logarithmic
probability paper, a value of logarithmic standard deviation
(.sigma..sub..zeta.), which is an index showing uniformity of a particle,
is 0.35 or less, in a more preferable case 0.30 or less, that is narrow
particle distribution not yet obtained by any previous method.
In the other side, when the viscosity of an aqueous solution of
water-soluble ethylenically unsaturated monomer is adjusted in a range of
5,000.about.1,000,000 cps, although dependent upon stirring condition, the
particles obtained shows that the ratio between average length and average
breadth for particles as defined as below-described is in a range of
1.5.about.20, and an angle-lacking and non-sphere, so to speak, Vienna
sausage-like shape. This polymer has length of 100.about.10000 .mu.m, more
preferably 1000.about.10000 .mu.m and breadth of 10.about.2000 .mu.m, more
preferably 100.about.2000 .mu.m, and a ratio between average length and
average breadth being in a range of 1.5.about.20, so that it is easy in
handling and treating in point of that it is hard for this polymer to fall
off from basis materials, and the range of the combination with different
basis materials is spread. The diameters to represent a shape of
water-absorbent polymer are defined as follows.
##STR1##
Although being in a range of 5,000 cps or more, when the viscosity is in a
range of 5,000.about.20,000 cps, a non-sphere polymer and a sphere polymer
are obtained as a mixture and, when the viscosity is higher than 20,000
cps, a non-sphere polymer is only obtained. Furthermore, when the
viscosity is higher than 1,000,000 cps, there is sometimes accompanied by
difficulty when an aqueous solution of monomer being supplied for a
reaction vessel.
As the thickener used for adjsting viscosity as described above, are cited
hydroxyethylcellulose, hydroxypropylcellulose, methylcellulose,
carboxymethylcellulose, polyethylene glycol, polyacrylamide,
polyethyleneimine, polyacrylic acid, partially neutralized polyacrylic
acid, crosslinked polyacrylic acid, partially neutralized, crosslinked
polyacrylic acid, dextrin, and sodium arginate so on. Preferable are
hydroxyethylcellulose, polyacrylamide, polyacrylic acid, partially
neutralized polyacrylic acid, crosslinked polyacrylic acid, partially
neutralized, crosslinked polyacrylic acid. Very specially preferred for a
water absorbent-resin having a new shape is hydroxyethylcellulose. For use
of a water-soluble, partially neutralized polyacrylic acid, the viscosity
of its 5% aqueous solution is preferred when it is 30 cps or more. For use
of a water-insoluble, crosslinked product, is preferred the one whose
particle diameter is about 30 .mu.m or less and powder-like.
To thicken an aqueous solution to a designated viscosity by using these
thickener, it is preferred that the thickener is generally used in a range
of 0.05.about.20 weight % to a monomer, although the percentage is
variable with the kind and concentration of a monomer and the kind and
molecular weight of a thickener.
In the other side dispersing agents used in this case are sucrose fatty
acid esters and/or polyglycerol fatty acid esters. As the former sucrose
fatty acid esters, are cited mono-, di-, and triesters derived from
sucrose with more than one aliphatic acid chosen from stearic acid,
palmitic acid, lauric acid, and oleic acid. As the latter polyglycerol
fatty acid esters, are cited mono-, di-, and triesters derived from
polyglycerin of condensation degree 10 or less with, at least, one
aliphatic acid chosen from stearic acid, palmitic acid, lauric acid, oleic
acid, and ricinolic acid. Among all these nonionic surface active agents,
most preferable are those indicating HLB of 2.about.6. The amount of a
dispersing agent for use is generally 0.05.about.10 weight %, more
preferably 0.5.about.5 weight % against the amount of a water-soluble
ethylenically unsaturated monomer. To obtain the water-absorbent polymer
having a new non-sphere shape without angle, that is one of the polymers
suitable for use in the present invention, the sucrose fatty acid esters
can be only used and, if other kinds of dispersing agents are used, this
novel type of resin is not obtained.
As an inert hydrophobic organic solvent used for the present invention are
cited, for example, aliphatic hydrocarbons such as n-pentane, n-hexane,
n-heptane, and n-octane; cycloaliphatic hydrocarbons such as cyclohexane,
cyclooctane, methylcyclohexane, decaline, and their derivatives; aromatic
hydrocarbons such as benzene, ethylbenzene, toluene, xylene, and their
substituted derivatives; and halogenated hydrocarbons such as
chlorobenzene, bromobenzene, carbon tetrachloride, and 1,2-dichloroethane.
These agents can be used as alone or a mixture of two kinds or more.
Specially preferable are n-hexane, n-heptane, cyclohexane,
methylcyclohexane, toluene, xylene, and carbon tetrachloride.
The ratio of an organic solvent to a water-soluble ethylenically
unsaturated monomer is generally suitable as 1:1.about.5:1 from
standpoints of steady dispersion and removal of heat generated during
polymerization and temperature controll.
As an initiator for radical polymerization in the present invention, any
kind of conventional agent can be used without limitation, but
particularly, water-soluble ones are preferred. More concretely, for
example, persulfates such as potassium persulfate, sodium persulfate, and
ammonium persulfate; hydroperoxides such as hydrogen peroxide, t-butyl
hydroperoxide, and cumene hydroperoxide; azo compounds such as
2,2'-azo-bis-2-amidinopropane dihydrochloride etc. are cited. These
polymerization initiators can be used as a mixture of more than two
agents. Furthermore, a redox type initiator prepared by combination of
these polymerization initiators and reducing agents such as sulfite,
L-ascorbic acid, and ferric salts may also be used.
In the case where above-described reverse-phase suspension polymerization
is performed to obtain a water-absorbent polymer used for the present
invention, if it is followed by a drying process, a water-absorbent
polymer obtained can be taken out as a bead-like or Vienna sausage-like
particle. As this drying process, there are methods wherein water is
distilled off as an azeotropic mixture with a hydrophobic organic solvent
used in polymerization and wherein filtration of a water-containing gel
followed by drying with conventional drying apparatus due to heated wind,
reduced pressure, or fluid bed is carried out.
To obtain a polymer powder usable in this invention, not only the
above-described reverse-phase suspension polymerization, but also an
usable condition is that, when a water-containing gel obtained from an
aqueous solution polymerization known in public is dried, pulverized, and
classified, the average particle diameter is adjusted in a range of
100.about.600 .mu.m and the particle diameter distribution is adjusted at
a value of 0.35 or less of .sigma..sub..zeta..
This invention is attained with uniform quality improvement of a polymer
surface by means of surface-crosslinking in a previously known method
where the polymer having an average particle diameter in a specially
defined range, a narrow distribution of particle diameters, and a sausage
shape are obtained according to the above-described method.
A more preferable method is that a polymer powder obtained by drying up to
less than 10 weight % of water content is mixed with 0.005.about.20 weight
% of a crosslinking agent (against the polymer powder) having a reactive
group of two or more in its molecule for a functional group in the powder,
a reaction is carried out with heating, and said polymer powder is
crosslinked in a neighbor of the surface. When the crosslinking agent and
the polymer powder being mixed, it is permitted to contain water and a
hydrophiric organic solvent.
When this surface-crosslinking treatment being performed, if the treatment
condition is chosen from a specially defined ones, the treatment effect
becomes superior and an advantage of this process increases. That is, a
polymer powder of water content of less than 10 weight % is mixed with a
treatment solution composed of 0.005.about.20 weight % (more preferable
0.005.about.5 weight %) of a crosslinking agent to the polymer powder,
0.1.about.5 weight % of water, and 0.01.about.6 weight % of hydrophilic
organic solvent, and thereby, the surface and its neighborhood of polymer
power being crosslinked.
When the polymer powder having been obtained from the previously-described
procedure, having an average particle diameter in the specially defined
range, and showing narrow distribution of particle diameter is mixed with
a treatment solution containing a crosslinking agent, any fish eye is not
formed, the treatment solution is uniformly dispersed on the surface of
the polymer powder, and appropriately permeated in a neighborhood of the
polymer powder surface, and as a result, the crosslinking is performed
uniformly and with good efficiency. Thus, is obtained a water-absorbent
resin wherein water-absorption capacity being high, water-absorption rate
and suction force being superior, elution of a water-soluble composition
from the resin being small in amount, and as a sanitary material, being
very suitable.
In the above described crosslinking process for producing a water-absorbent
resin in this invention it is first required to maintain water content of
the polymer at a value less than 10%, more preferably less than 7% by the
similar process as the above-described one, which was obtained with
reverse-phase suspension polymerization. In a case of water content 10% or
more, when a crosslinking agent or the treatment solution containing this
is mixed, in addition to that the mixing character is inferior, the
crosslinking agent sometimes super-permeates an inside of the resin, so
that a water-absorbent resin obtained sometimes has small water-absorption
capacity.
As a crosslinking agent, which is able to use in this invention, although
unlimited as far as it is a compound having two or more of a functional
group reactive with functional groups existing in the polymer, are
preferred hydrophilic, more preferred water-soluble compounds. For
examples, in a case that the polymer has a carboxyl and/or carboxylate
group as a functional group, are cited polyhydric alcohols such as
ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene
glycol, polyethylene glycol, glycerol, polyglycerol, propylene glycol,
diethanolamine, triethanolamine, polyoxypropylene, oxyethyleneoxypropylene
block copolymer, pentaerythritol, and sorbitol; polyglycidyl compounds
such as ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl
ether, glycerol polyglycidyl ether, diglycerol polyglycidyl ether,
polyglycerol polyglycidyl ether, sorbitol polyglycidyl ether,
pentaerythritol polyglycidyl ether, propylene glycol diglycidyl ether, and
polypropylene glycol diglycidyl ether; polyaziridine derivatives such as
2,2'-bishydroxymethylbutanol-tris [3-(1-aziridinyl) propionate],
1,6-hexamethylenediethylenyl urea, and
diphenylmethane-bis-4,4'-N,N'-diethylenyl urea; haloepoxy compounds such
as epichlorohydrine and .alpha.-methylchlorohydrine; polyaldehydes such as
glutal aldehyde and glyoxal; polyamine derivatives such as
ethylenediamine, diethylenetriamine, triethylenetetramine,
tetraethylenepentamine, pentaethylenehexamine, and polyethyleneimine;
polyisocyanates such as 2,4-toluylenediisocyanate and
hexamethylenediisocyanate; polyvalent metal salts such as aluminium
chloride, magnesium chloride, calcium chloride, aluminium sulfate,
magnesium sulfate, and calcium sulfate. Paticularly preferable are
polyhydric alcohols, polyglycidyl compounds, polyamine derivatives, and
polyvalent metal salts. The amount of use of these hydrophilic
crosslinking agent is 0.005.about.20 weight % against a polymer powder,
preferable 0.005.about.5 weight %, more preferable 0.01.about.1 weight %.
In a case that this amount is less than 0.005 weight %, an effect of
surface treatment does not appear and also, even if it is used in amount
more than 20 weight %, there are some cases where an effect correspond to
amount of use of crosslinking agent does not appear and the water
absorption capacity remarkably decreases.
In the present invention, if a crosslinking agent is mixed with polymer
powder, it is preferable for increase of the treatment effect that the
above-described treatment solution containing water and an organic solvent
is used. In this case, the amount of water composing a treatment solution
is 0.1.about.5 weight % against a polymer powder. If this amount is less
than 0.1 weight %, a crosslinking agent does not easily permeate a
neighborhood of the polymer powder surface, so that a crosslinking surface
layer does not properly form. Also, there are some cases where if it
exceeds 5 weight %, the agent permeats in exess, so that the water
absorption capacity decreases.
As a hydrophilic organic solvent composing of the treatment solution, it is
not particularly limited as far as it can dissolve a crosslinking agent
and does not affect the performance of a water-absorbent resin. As such,
for examples, are cited lower alcohols such as methanol, ethanol,
n-propanol, isopropanol, and n-butanol; ketones such as acetone and
methylethylketone; ethers such as dioxane and tetrahydrofuran; amides such
as N-N'-dimethylformamide; sulfoxides such as dimethylsulfoxide. The
amount of use of a hydrophilic organic solvent is 0.1.about.6 weight %. In
a case that the amount of use of a hydrophilic organic solvent is less
than 0.1 weight %, mixing of a polymer with the treatment solution becomes
nonuniform and also, if the amount exeeds 6 weight %, an effect
corresponding to the amount of use can not be obtained and only expense
increases, so that it is not industrially favorable. Although dependent
upon the kind of hydrophilic organic solvents, it is generally preferable
to use 0.3.about.4 weight % against a water-absorbent resin.
As a method to mix a treatment solution containing a crosslinking agent
with a polymer powder in this invention, it is general to spray or drop
and mix the treatment solution for a polymer powder. As a mixer used for
mixing, although is preferred the one having a big mixing power to mix
uniformly, conventional mixer and kneader can be used. For examples, are
cited a cylinder mixer, a double cone mixer, a V-type mixer, a ribbon
mixer, a screw mixer, a fluidized mixer, a rotating-disc type mixer, an
air mixer, a double-arm type kneader, an internal mixer, a muller kneader,
a roll mixer, and a screw extruder etc. To warm up a composition obtained
with mixing a treatment solution containing these crosslinking agents with
a polymer powder, a conventional dryer or heating furnace can be used. For
examples, are cited a gutter stirring dryer, a rotating dryer, a disc
dryer, a kneading dryer, a fluidized dryer, an air dryer, an infrared
light dryer, and an dielectrically heating dryer. Temperature for heating
treatment is in a range of 40.degree..about.250.degree. C., more
preferable 80.degree..about.200.degree. C.
The water-absorbent resin obtained from the production process in this
invention has an average particle diameter in a specially defined range
and a narrow distribution of particle diameter and also, has high water
absorption capacity and a superior water absorption rate and suction
force. In addition, since a water-soluble component existing in an inside
of the resin is only eluted in a very small amount from a surface of the
resin, the resin is very superior, in particular, in a dispersion
character of liquid and in safety when being used as sanitary materials.
This kind of water-absorbent resin, as mentioned above, is possible to be
produced in the best yield and with high efficiency in the case of that an
aqueous solution of water-soluble ethylenically unsaturated monomer, of
which viscosity is adjusted at a specially defined value by using a
thickener, undergoes a reverse-phase suspension polymerization using a
sucrose fatty acid ester and/or polyglycerol fatty acid ester as a
dispersing agent and a polymer obtained is dried and, mixed and warmed
with a treatment solution containing a crosslinking agent of a specially
defined composition.
Also, such a method involving treatment of a surface part like this case
does not require a large amount of organic solvent, so that it is of
advantage to economy and industry and a superior water-absorbent resin
being of high safety as a sanitary material and various kinds of
water-holding materials became obtainable in a method very useful for
producing.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an optical microphotograph to represent a particle structure of
the water-absorbent resin of a sphere shape (A16) obtained from example 6.
FIG. 2 is an optical microphotograph to represent a particle structure of
the water-absorbent resin of a vienna sausage shape (A18) obtained from
example 8.
FIG. 3 is an optical microphotograph to represent a particle structure of
the water-absorbent resin (B12) obtained from example for comparison 3.
DETAILED DESCRIPTION OF THE INVENTION
Examples
Although the present invention is explained in detail with the examples
described below, a range of the present invention is not defined within
the examples.
The water absorption performance of water-absorbent resin is determined
according to the procedure shown below.
(1) Average Particle Diameter and Distribution of Particle Diameter
The resin powder is sifted and classified by using JIS standard sieves (20,
32, 48, 60, 100, 145, 200, and 350 mesh) and then, the remaining
percentage (R %) is plotted on a logarithmic probability paper. Average
diameter is represented by a particle diameter corresponding to R for 50%.
The particle distribution is represented by using logarithmic standard
deviation, .sigma..sub..zeta., as an index, which is derived from the
following equation:
##EQU1##
Here, it is meaned that, as the value of .sigma..sub..zeta. becomes
smaller, the particle distribution becomes more uniform.
(2) Water Absorption Capacity
The water-absorbent resin, 0.2 g, is uniformly put into a tea bag-like bag
(40 mm.times.150 mm) made by a nonwoven fabric, and soaked in a 0.9 weight
% aqueous solution of sodium chloride. The teabag-like bag is taken out
after 10 minutes and 30 minutes, respectively, and stood for draining for
a designated time. Then, the weight is determined and the water absorption
capacity is calculated by the following equation. Further, when only the
tea bag is being soaked, the weight obtained after water absorption is
taken as a blank.
Water absorption capacity (g/g)=(weight of bag after
absorption-blank)/(weight of water-absorption resin).
(3) Water Absorption Rate
To 20 ml of synthetic urine containing 1.9 weight % of urea, 0.8 weight %
of sodium chloride, 0.1 weight % of calcium chloride, and 0.1 weight % of
magnesium sulfate is added 1.0 g of a water-absorbent resin. The water
absorption rate is defined with time passed until the water-absorbent
resin absorbing the synthetic urine losts the flowing character of a
swelling gel.
(4) Suction force
Water-absorbent resin, 1.0 g, is placed on a material containing synthetic
urine, prepared by adding 20 ml of synthetic urine on a tissue paper of
size 55 mm.times.75 mm. After standing for 10 minutes, a gel swelled is
taken and weighed. The weight is defined as suction force of the resin
from the tissue paper. At the same time, the presence of a fish-eye of the
added water-absorbent resin was examined.
(5) Amount of Water-Soluble Component Eluted from Resin Surface
A disposable diaper for child composed of a nonwoven fabric, cotton-like
pulp, a water-absorbent paper, and a waterproof film (having a weight of
72 g) is cut in half and 2.5 g of a polymer is uniformly scattered between
the cotton-pulp and the water-absorbent paper and to this, 120 ml of the
above-described synthetic urine is added, and the thus-prepared sample is
stood for 16 hours at 37.degree. C. After standing for 16 hours, the
cotton-like pulp is only taken and a water-soluble component transferred
from the pulp is extracted with 1,000 ml of pure water. This extract
solution is filtered and a polymer component contained in this filtered
solution is measured by using an acid-base titration method and thus, a
total amount of a water-soluble component eluted is determined against the
amount of water-absorbent resin as weight %.
EXAMPLE 1
In a four-necked separable 2 L flask equipped with a stirrer, a reflux
condenser, a thermometer, an inlet tube for nitrogen gas, and a dropping
funnel was placed 1,000 ml of cyclohexane and dissolved 4.0 g of a sucrose
fatty acid ester (DKESTER F-50, HLB=6, a product from DAIICHI KOGYO
SEIYAKU Co., LTD.) and nitrogen gas was introduced into this solution to
remove oxygen dissolved. In another flask containing a solution of 84.6 g
of sodium acrylate, 21.6 g of acrylic acid, and 0.016 g of
N,N'-methylene-bisacrylamide in 197 g of ion-exchanged water was dissolved
0.53 g of hydroxyethylcellulose (HEC-DAISERU EP-850, a product from
DAISERU CHEMICAL Co., LTD.) and was prepared a monomer solution adjusted
at a monomer concentration of 35 weight % and viscosity of 40 cps. To this
monomer solution was dissolved 0.15 g of potassium persulfate and then,
nitrogen gas was introduced to remove oxygen dissolved in this aqueous
solution.
Next, to the above separable flask solution was added the aqueous monomer
solution in the latter flask and the mixture obtained was dispersed with
stirring at 230 rpm. Then, polymerization reaction was initiated by
raising bath temperature to 60.degree. C. and completed by maintaining
this temperature for 2 hours. After polymerization, the reaction mixture
was treated by an azeotropic distillation with cyclohexane to remove water
in the water-containing gel, filtered, and dried at 80.degree. C. under
reduced pressure to obtain a polymer powder of sphere shape (A01). Water
content for this polymer powder was 5.6%.
With 100 weight parts (weight parts are hereinafter referred to as parts)
of the polymer powder (A01) was mixed by a paddle type mixer a treatment
solution composed of 0.3 parts of diethylene glycol, 4 parts of water, and
0.5 parts of isopropanol. When mixing, any large lump is not formed and
all the composition passed through a 20 mesh metal net (mesh of 840 .mu.m)
when tried. The composition obtained was treated with heat by a paddle
type dryer at 180.degree. C. for 1 hour to obtain a water-absorbent resin
(A11). Results obtained from properties measurements for this resin are
shown in table 1.
EXAMPLE 2
Except the use of 2.2 g of hydroxyethylcellulose (SP600, a product from
DAISERU CHEMICAL Co., LTD.), a polymerization reaction was carried out
under the same conditions to those for example 1. Viscosity of the monomer
aqueous solution was 800 cps and water content of a polymer powder of
sphere shape (A02) was 6.8%. With 100 parts of the polymer powder (A02)
was mixed by a paddle type mixer a treatment solution composed of 0.1
parts of ethylene glycol diglycidyl ether, 3 parts of water, and 6 parts
of methanol. When passing is tried, all the composition passed through a
20 mesh metal net. The composition obtained was treated with heat by a
paddle type dryer at 100.degree. C. for 1 hour to obtain a water-absorbent
resin (A12). Results obtained from properties measurements for this resin
are shown in table 1.
EXAMPLE 3
Except the use of 3.5 g of hexaglycerol-condensed ricinolate (STEP RP-6, a
product from KAO Co., LTD.), a polymerization reaction was carried out in
the same way as in example 1 to obtain a polymer powder of sphere shape
(A03), which showed water content of 6.3%. With 100 parts of the polymer
powder (A03) was mixted by a V-type mixer a treatment solution composed of
0.08 parts of epichlorohydrin, 2 parts of water, and 4 parts of methanol.
When tried, all the composition passed through a 20 mesh metal net and a
lump is not observed which may be formed when mixing. The composion
obtained was treated with heat by a paddle type dryer at 100.degree. C.
for 1 hour to obtain a water-absorbent resin (A13). Results obtained from
properties measurements for this resin are shown in table 1.
EXAMPLE 4
In a four-necked separable 2 L flask equipped with a stirrer, a reflux
condenser, a thermometer, an inlet tube for nitrogen gas, and a dropping
funnel was placed 1,000 ml of cyclohexane and dissolved 4.0 g of a sucrose
fatty acid ester (DKESTER F-20, a product from DAIICHI KOGYO SEIYAKU Co.,
LTD.), and nitrogen gas was introduced into this solution to expel oxygen
dissolved. In another flask, 65.8 g of sodium acrylate, 21.6 g of acrylic
acid, 0.076 g of polyethylene glycol diacylate (n=14), and 15 g of sodium
polyacrylate (AQUALIC OM-100, a product from NIPPON SHOKUBAI KAGAKU KOGYO
Co., LTD., viscosity of 150 cps at 25.degree. C. for a 5% aqueous
solution) was dissolved in 250 g of ion-exchanged water to prepare an
aqueous monomer solution of viscosity of 20 cps.
Next, into this solution, 0.12 g of sodium persulfate was dissolved and a
reaction procedure was carried out in the same way as that for example 1
to obtain a polymer powder of sphere shape (A04), which showed water
content of 4.8%.
With 100 parts of the polymer powder (A04) was mixed by a paddle type mixer
a treatment solution composed of 1 part of glycerol, 5 parts of water, and
1 part of isopropanol. All the composition passed through a 20 mesh metal
net and any lump is not formed at the mixing. Then, the composition
obtained was treated with heat by a paddle type dryer at 180.degree. C.
for 1.5 hours to obtain a water-absorbent resin (A14). Results obtained
from properties measurements for this resin are shown in table 1.
EXAMPLE 5
Except the use of sodium polyacrylate (AQUALIC FH, 2.times.10.sup.4 cps at
25.degree. C. for viscosity of 1% aqueous solution, a product from NIPPON
SHOKUBAI KAGAKU KOGYO Co., LTD.) as a thickener, a reaction procedure was
carried out in the same way as that for example 4 to obtain a polymer
powder of sphere shape (A05), showing water content of 5.8%. The viscosity
of an aqueous monomer solution was 27 cps. With 100 parts of the polymer
powder (A05) was mixed by a ribbon type mixer a treatment solution
composed of 0.05 parts of glycerol glycidyl ether, 4 parts of water, and
0.8 parts of ethanol. All the composition passed through a 20 mesh metal
net and, when mixing, any lump did not form. The composition obtained was
treated with heat in a fluidized bed dryer at 100.degree. C. for 1 hour to
obtain a water-absorbent resin (A15). Results obtained from properties
measurements for this resin are shown in table 1.
EXAMPLE 6
Except that the amount of hydroxyethylcellulose (HEC-DAISERU EP-850, a
product from DAISERU KAGAKU KOGYO Co., LTD.) in example 1 was changed into
1.6 g and the viscosity of aqueous monomer solution was adjusted at 2,000
cps, a polymerization reaction was carried out in the same way as that for
example 1 to obtain 0.6 g of a water-absorbent polymer powder of all
sphere shape (A06), which showed water content of 6.4%. In the same way as
carried out for example 1, this polymer powder (A06) was treated with a
surface crosslinking to obtain a water-absorbent resin (A16). Results
obtained from properties measurements for this resin are shown in table 1.
EXAMPLE 7
Except that the amount of hydroxyethylcellulose (HEC-DAISERU SP-600, a
product from DAISERU KAGAKU KOGYO Co., LTD.) was 0.3 g and the viscosity
of aqueous monomer solution was adjusted at 17 cps, a polymerization
reaction was carried out in the same way as that for example 2 to obtain a
water-absorbent polymer powder of sphere shape (A07) which showed water
content of 5.9%. In the same way as carried out for example 1, this
polymer powder (A07) was treated with a surface crosslinking to obtain a
water-absorbent resin (A17).
Results obtained from properties measurements for this resin are shown in
table 1.
EXAMPLE 8
In a four-necked separable 2 L flask equipped with a stirrer, a reflux
condenser, a thermometer, an inlet tube for nitrogen gas, and a dropping
funnel is placed 1,000 ml of cyclohexane and dissolved 4.0 g of a sucrose
fatty acid ester (DK-ESTER F-50, a product from DAIICHI KOGYO SEIYAKU Co.,
LTD., HLP=6) and nitrogen gas was introduced into this solution to remove
oxygen dissolved. In another flask containing a solution of 84.6 g of
sodium acrylate, 21.6 g of acrylic acid, and 0.016 g of
N,N'-methylene-bisacrylamide in 197 g of ion-exchanged water was dissolved
3.2 g of hydroxyethylcellulose (HEC-DAISERU EP-850, a product from DAISERU
CHEMICAL Co., LTD.) and was prepared an aqueous monomer solution adjusted
at a monomer concentration of 35 weight % and viscosity of 35,000 cps. To
this aqueous monomer solution was dissolved 0.15 g of potassium persulfate
and then, nitrogen gas was introduced to remove oxygen dissolving in this
aqueous solution.
Next, to the above separable flask solution was added the aqueous monomer
solution in the latter flask and the mixture obtained was dispersed with
stirring at 230 rpm. Then, polymerization reaction was initiated by
raising bath temperature to 60.degree. C. and completed by maintaining
this temperature for 2 hours. After polymerization completed, the reaction
mixture was treated by an azeotropic distillation with cyclohexane to
remove water in the water-containing gel, filtered, and dried at
80.degree. C. under reduced pressure to obtain a polymer powder (A08),
which had average length of 3,000 .mu.m and average breadth of 550 .mu.m
and showed somewhat long and narrow shape of Vienna sausage type. Besides,
any sphere particle did not exist.
This polymer powder (A08) was treated with surface crosslinking in the same
way as that for example 1 to obtain a water-absorbent resin (A18). Results
obtained from properties measurements for this resin are shown in table 1.
EXAMPLE 9
Except that the amount of a thickener, hydroxyethylcellu lose (EP-850, a
product of DAISERU KAGAKU KOGYO Co., LTD.) was changed into 5.3 g, a
polymerization reaction was carried out in the same way as that for
example 8. Viscosity of the aqueous monomer solution was 240,000 cps.
After the polymerization completed, treatment with an azeotropic
dehydration followed by filtration and drying under reduced pressure gave
a polymer powder (A09) having average length of 3500 .mu.m and average
breadth of 600 .mu.m and showing a long and narrow shape of Vienna sausage
type. Any sphere particle did not exist. This polymer powder (A09) was
treated with surface crosslinking in the same way as that for example 2 to
obtain a water-absorbent resin (A19). Results obtained from properties
measurements for this resin are shown in table 1.
EXAMPLE 10
Into 329 g of ion-exchanged water was dissolved 141 g of sodium acrylate,
36.1 g of acrylic acid, and 0.118 g of N,N'-methylen-bisacrylamide and, a
static aqueous solution polymerization was carried out at
55.degree..about.80.degree. C. under a nitrogen atmosphere by using 0.68 g
of ammonium persulfate and 0.025 g of sodium hydrogensulfite to obtain a
gel-like water-containing polymer, which was dried at 180.degree. C. with
a heated wind dryer, pulverized with a hammer-type pulverizer, and sieved
with a 28 and a 60 mesh metal nets. The portion, which passed the 28 mesh
net but not the 60 mesh net, was taken as a pulverized polymer powder
(A010). Treatment of this polymer powder (A010) by surface crosslinking
performed in the same way as that for examle 1 gave a water-absorbent
resin (A110). Results obtained from properties measurements for this resin
are shown in table 1.
EXAMPLE for COMPARISON 1
Properties of the polymer powder (A01) obtained from example 1 were
measured and summarized in table 1.
EXAMPLE for COMPARISON 2
Except that 3.5 g of sorbitane monostearate (REODOL SP-S10, a product from
KAO Co., LTD.) was used as a dispersing agent instead of a sucrose fatty
acid ester, a polymerization procedure was carried out in the same way as
for example 1 to obtain a polymer powder for comparison (B01), which had
water content of 6.2%. The polymer powder for comparison (B01) obtained
was mixted with a liquid composition, which is the same as used for
example 1, by a paddle type mixer. When mixing, were formed lumps in 8.6%,
which did not pass through a 20 mesh metal net. The composition obtained
was treated with heat at 180.degree. C. for 1 hour by using a paddle dryer
to obtain a water-absorbent resin for comparison (B11). Results obtained
from properties measurements for this resin are shown in table 1.
EXAMPLE for COMPARISON 3
Except no addition of hydroxyethylcellulose to a aqueous monomer solution,
the same procedure as for example 1 was carried out to obtain a polymer
powder (B02), which showed water content of 4.7%. At this time, viscosity
of a aqueous monomer solution was 7 cps.
The polymer powder for comparison (B02) was mixed by a paddle type mixer
with a liquid composition same as used in example 2. When mixing, were
formed lumps in 8.2% which did not pass through a 20 mesh metal net. The
composition obtained was treated with heat by a fluidized bed dryer at
100.degree. C. for 1 hour to obtain a water-absorbent resin for comparison
(B12). Results obtained from properties measurements for this resin are
shown in table 1.
EXAMPLE for COMPARISON 4
Except that 4.0 g of tetraglycerol monostearate (POEMU J-4010, a product
from RIKEN VITAMIN Co., LTD.) was used as a dispersing agent instead of a
sucrose fatty acid ester used in example 1 and hydroxyethylcellulose was
not added to the aqueous monomer solution, a procedure same as for example
1 was carried out to obtain a polymer powder (B03), which showed water
content of 5.9%.
The polymer powder for comparison (B03) was mixed with a liquid
composition, which is the same as used for example 1, by a paddle type
mixer. When mixing, were formed lumps in 7.6% which did not pass through a
20 mesh metal net. The composition was treated with heat by a paddle dryer
at 180.degree. C. for 1 hour to obtain a water-absorbent resin for
comparison (B13). Results obtained from properties measurements for this
resin are shown in table 1.
EXAMPLE for COMPARISON 5
Properties measured for the polymer powder (A08) in example 8 are shown in
table 1.
EXAMPLE for COMPARISON 6
In example 10, taking only a part passed through a 28 meth metal net, a
polymer powder for comparison (B04) was obtained. Treatment of this
polymer powder for comparison (B04) with surface-crosslinkage gave a
water-absorbent resin for comparison (B14). Results obtained from
properties measurements for this resin are shown in table 1.
TABLE 1
__________________________________________________________________________
Average
Particle
particle
diameter
Amount
Water absorption
Water-absorbent resin
diameter
distribution
of lump
capacity (g/g)
obtained (.mu.m)
.sup..sigma. .zeta.
(%) 10 min.
30
__________________________________________________________________________
min.
Example 1 Water-absorbent resin (A11)
400 0.16 0 59 65
Example 2 Water-absorbent resin (A12)
500 0.11 0 54 60
Example 3 Water-absorbent resin (A13)
300 0.15 0 57 63
Example 4 Water-absorbent resin (A14)
350 0.18 0 60 67
Example 5 Water-absorbent resin (A15)
350 0.17 0 59 65
Example 6 Water-absorbent resin (A16)
550 0.19 0 47 64
Example 7 Water-absorbent resin (A17)
150 0.24 0 52 60
Example 8 Water-absorbent resin (A18)
sausage-like shape
0 36 51
Example 9 Water-absorbent resin (A19)
sausage-like shape
0 38 54
Example 10 Water absorbent resin (A110)
280 0.16 0 43 62
Example for comparison 1
Polymer powder (A01) 400 0.16 -- 44 62
Example for comparison 2
Water-absorbent resin for comparison (B11)
80 0.43 8.6 45 56
Example for comparison 3
Water-absorbent resin for comparison (B12)
100 0.41 8.2 41 53
Example for comparison 4
Water-absorbent resin for comparison (B13)
150 0.40 7.6 43 55
Example for comparison 5
Water-absorbent resin for comparison (A08)
sausage-like shape
-- 28 50
Example for comparison 6
Water-absorbent resin for comparison (B14)
230 0.58 3.5 38 59
__________________________________________________________________________
Water-
Water soluble
absorption
Suction component
Water-absorbent resin
rate force
Formation
eluted
obtained (sec.)
(g) fish-eye*
(%)
__________________________________________________________________________
Example 1 Water-absorbent resin (A11)
21 18.0
.circleincircle.
0.15
Example 2 Water-absorbent resin (A12)
33 17.9
.circleincircle.
0.08
Example 3 Water-absorbent resin (A13)
28 18.8
.circleincircle.
0.12
Example 4 Water-absorbent resin (A14)
22 18.7
.circleincircle.
0.07
Example 5 Water-absorbent resin (A15)
19 18.2
.circleincircle.
0.05
Example 6 Water-absorbent resin (A16)
42 17.6
.circleincircle.
0.09
Example 7 Water-absorbent resin (A17)
18 18.2
.circleincircle.
0.13
Example 8 Water-absorbent resin (A18)
52 16.2
.circleincircle.
1.21
Example 9 Water-absorbent resin (A19)
49 16.3
.circleincircle.
0.99
Example 10 Water absorbent resin (A110)
38 17.8
.circleincircle.
1.82
Example for comparison 1
Polymer powder (A01) 65 13.2
.circle.
4.2
Example for comparison 2
Water-absorbent resin for comparison
4911) 15.2
.DELTA.
3.5
Example for comparison 3
Water-absorbent resin for comparison
4512) 15.1
.DELTA.
3.1
Example for comparison 4
Water-absorbent resin for comparison
4713) 14.8
.DELTA.
3.3
Example for comparison 5
Water-absorbent resin for comparison
9708) 11.3
.circle.
4.9
Example for comparison 6
Water-absorbent resin for comparison
4714) 15.0
.DELTA.
5.1
__________________________________________________________________________
(Note)*
.circleincircle.: No formation of fisheye at all.
.circle. : Nearly no formation of fisheye.
.DELTA.: Some formation of fisheye.
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